Optical print head positioning using mechanically coupled optical pickup unit

An optical print head (OPH) on the label side of an optical disc is positioned to a desired labeling position through a mechanical coupling between the OPH and an optical pickup unit (OPU) at the data side of the optical disc. The OPU is positioned to a target data track on the data side of the disc, and the OPH is moved to a desired label position through the mechanical coupling.

BACKGROUND

An optical disc is an electronic data storage medium that can be written to and read from using a low-powered laser beam. For example, a CD (compact disc) is typically used to record, store, and play back various media such as audio, video and text in digital form, while a DVD (digital versatile disc) is generally used for storing and playing back whole movies due to its increased storage capability.

Recordable and rewritable disc drives for both CDs and DVDs have become common place, enabling the average consumer to record and rewrite their own data onto their own CDs and DVDs by “burning” the data into, for example, CD-Rs (CD-recordable discs), CD-RWs (CD-rewritable discs), DVD+Rs (DVD-recordable discs), and DVD+RWs (DVD-rewritable discs). The ability to create personalized collections of data on CDs and DVDs has driven consumer desire for convenient ways to identify the data in such collections. Accordingly, methods for labeling the non-data side of optical discs (e.g., CDs, DVDs) have developed from physically writing on the non-data side of a disc with a permanent marker, for example, to using the laser in a conventional CD player to mark a specially prepared CD surface.

In general, a label image can be rendered on the label surface of an optical disc (i.e., the non-data side, or top side) by marking the label surface with a laser beam along concentric circles around the disc. For each circle, spots of constant size and optical density are marked by the laser according to marking data for that circle. However, because there are typically no markings or other reference points on the non-data/label side of a disc, accurately positioning the laser in the radial direction of the disc has remained a challenging problem.

DETAILED DESCRIPTION

Introduction

The following discussion is directed to disc media marking systems and methods that enable the positioning of an optical print head (OPH) at the label side, or non-data side (top side), of an optical disc for the precise spacing of label tracks printed by the OPH. A mechanical coupling between the OPH and an optical pickup unit (OPU) at the data side of the disc couples the motion of the OPU to the OPH. Thus, the positioning capability of the OPU is leveraged to accurately position the label-side OPH for printing a label onto the disc. Data side tracks are used to microstep the OPU sled on the data side of the disc which, in turn, provides precise positioning of the OPH at the label side of the disc through the mechanical coupling. Benefits of the described system and methods include the ability to leverage data track positioning information and OPU positioning capability and components (e.g., sled motor, fine actuator) already present in single-head disc marking systems to achieve precise spacing of label tracks printed by an OPH in a dual-head disc marking system.

Exemplary Environment

FIG. 1illustrates an exemplary embodiment of a disc media marking system100suitable for positioning an optical print head (OPH) at the non-data/label side of an optical disc using the positioning capability of, and a mechanical coupling to, an optical pickup unit (OPU) positioned at the data side of the disc. The exemplary disc media marking system100includes a disc media marking device102and a display device104. The disc media marking device102can be implemented as a stand-alone appliance device for labeling disc media. Alternatively, the disc media marking device102can be integrated as part of an optical media player or drive, such as a writable compact disc (CD) player that is implemented to label an optical disc as well as record data onto a CD-R (CD-recordable disc) and/or a CD-RW (CD-rewritable disc). Such writable CD devices may include, for example, a stand-alone audio CD player that is a peripheral component in an audio system, a CD-ROM drive integrated as standard equipment in a PC (personal computer), a DVD (digital versatile disc) player, and any number of similar embodiments.

Disc media marking device102includes one or more processors106(e.g., any of microprocessors, controllers, and the like) that process various instructions to control the operation of disc media marking device102and communicate with other electronic and computing devices. Disc media marking device102can be implemented with one or more memory components, examples of which include a random access memory (RAM)108, a disk storage device110, and non-volatile memory112(e.g., any one or more of a read-only memory (ROM)114, flash memory, EPROM, EEPROM, etc.).

Disk storage device110can include any type of magnetic or optical storage device, such as a hard disk drive, a magnetic tape, a recordable and/or rewriteable compact disc (CD-R, CD-RW), a recordable and/or rewriteable digital versatile disc (DVD+R, DVD+RW) and the like. The one or more memory components provide data storage mechanisms to store various information and/or data such as configuration information for disc media marking device102, graphical user interface information, and any other types of information and data related to operational aspects of disc media marking device102. Alternative implementations of disc media marking device102can include a range of processing and memory capabilities, and may include any number of differing memory components than those illustrated inFIG. 1.

Disc media marking device102includes a firmware component116that is implemented as a permanent memory module stored on ROM114, or with other components in disc media marking device102, such as a component of a processor106. Firmware116is programmed and distributed with disc media marking device102to coordinate operations of the hardware within disc media marking device102and contains programming constructs used to perform such operations.

An operating system118and one or more application programs can be stored in non-volatile memory112and executed on processor(s)106to provide a runtime environment. A runtime environment facilitates extensibility of disc media marking device102by allowing various interfaces to be defined that, in turn, allow the application programs to interact with disc media marking device102. In this example, the application programs include a label design application120, an image processing application122, and a print control application124.

The label design application120generates a label design user interface126for display on display device104from which a user can create a label image to be rendered on a disc media, such as on an optical disc. A user can specify, or otherwise drag-and-drop text, a bitmap image for background, a digital photo, a graphic or symbol, and/or any combination thereof to create the label image on the user interface126.

The image processing application122processes the label image created with the label design user interface126to produce a data stream of label image data and laser control data to control rendering the image on concentric circular or spiral tracks of a disc media, such as optical disc204(FIGS. 2-4). For example, a continuous tone RGB (red, green, and blue) rectangular raster graphic of the label image can be converted to concentric circular tracks. The curved raster is color mapped and separated into the printing color channels KCMY (black, cyan, magenta, and yellow), or grayscale. This data stream is formatted as laser control data and is augmented with other control commands to control the disc media marking device102rendering a label on the optical disc204(FIGS. 2-4). A label file is generated that can be communicated to a controller where the label file is parsed to control a labeling mechanism. Alternatively, the concentric circular tracks may be generated and streamed to the disc media marking device102one track at a time to utilize host processing with the device's rendering process.

The print control application124determines the radius of the first track and the subsequent track spacing. After the radius of the first track and the track spacing are determined, the print control application124determines which label image data will correspond to each respective track. The laser mark locations along a particular track are specified in a coordinate system where the concentric circular tracks are defined in coordinates of the radial distance and the distance along each respective track.

Disc media marking device102includes a disc drive system128that can be implemented to mark on a surface of a disc media (i.e., optical disc), such as to render a label image on a label surface208(e.g., the non-data side) of optical disc204(FIGS. 2-4). The disc drive system128is described in greater detail herein below with reference toFIG. 2.

Disc media marking device102further includes one or more communication interfaces130that can be implemented as any one or more of a serial and/or parallel interface, as a wireless interface, any type of network interface, and as any other type of communication interface. A wireless interface enables disc media marking device102to receive control input commands and other information from an input device, such as from a remote control device or from another infrared (IR), 802.11, Bluetooth, or similar RF input device. A network interface provides a connection between disc media marking device102and a data communication network that allows other electronic and computing devices coupled to a common data communication network to send label image data and other information to disc media marking device102via the network. Similarly, a serial and/or parallel interface provides a data communication path directly between disc media marking device102and another electronic or computing device.

Disc media marking device102may include user input devices132that can include a keyboard, pointing device, selectable controls on a user control panel, and/or other mechanisms to interact with and input information to disc media marking device102. Disc media marking device102also includes an audio/video processor134that generates display content for display on display device104, and generates audio content for presentation by a presentation device, such as one or more speakers (not shown). The audio/video processor134can include a display controller that processes the display content to display corresponding images on display device104. A display controller can be implemented as a graphics processor, microcontroller, integrated circuit, and/or similar video processing component to process the images. Video signals and audio signals can be communicated from disc media marking device102to display device104via an RF (radio frequency) link, S-video link, composite video link, component video link, or other similar communication link.

Although shown separately, some of the components of disc media marking device102may be implemented in an application specific integrated circuit (ASIC). Additionally, a system bus (not shown) typically connects the various components within disc media marking device102. A system bus can be implemented as one or more of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, or a local bus using any of a variety of bus architectures. Furthermore, disc media marking device102may share a system bus with a host processor.

Exemplary Embodiments

FIG. 2illustrates an exemplary embodiment of the disc drive system128shown inFIG. 1as a component of the exemplary disc media marking device102. The disc drive system128includes a first, data-side laser assembly200generally configured to read data from and write data to data tracks on the data side202of an optical disc204. The disc drive system128also includes a second, label-side laser assembly206generally configured to write labels onto the label side or non-data side208of optical disc204. The data-side laser assembly200includes a sled210that supports optical pickup unit212(OPU). OPU212includes laser214, laser focusing lens and actuator216, fine actuator218, lens supports220, and sensing photodiode221. The label-side laser assembly206includes optical print head (OPH)222, which includes OPH laser224and detector225.

The disc drive system128also includes a spindle motor226, step motor228, and control unit230. Control unit230may be implemented, for example, as a printed circuit board employing a combination of various components discussed above with respect to the disc media marking system100ofFIG. 1. Accordingly, control unit230includes a processor232for processing computer/processor-executable instructions from various components stored in a memory234. Processor232is typically one or more of the processors106discussed above with respect to the disc media marking system100ofFIG. 1. Likewise, memory234is typically the non-volatile memory112and/or firmware116from the disc media marking system100ofFIG. 1.

Controllers236generally include laser controllers, a sled controller, actuator controllers, and a spindle controller that are stored in memory234and executable on processor232. A spindle controller drives spindle motor226to control a rotational speed of disc204via spindle238. Spindle controller236operates in conjunction with a sled controller236that drives the step motor228to control coarse radial positioning of sled210(i.e., laser assembly200, sled210, OPU212, laser214, etc.) with respect to disc204along a sled drive mechanism240. In turn, a mechanical coupling242translates the coarse positioning movements of the OPU212to the OPH222on the label side208of disc204.

In general, once the OPH222is properly positioned, OPH laser beam244is generated by OPH laser222and focused onto the label surface208of optical disc204. The OPH laser beam244creates laser marks that correspond to label image data to render an image of the label on the optical disc204as the disc rotates. When marking a label on disc204, the rotational speed of disc204and the radial position of OPH222and OPH laser224are typically controlled such that laser marks are written onto the disc204as the label surface208moves past the laser beam244at a constant linear velocity. A laser controller236controls the firing and intensity of OPH laser beam244to write laser marks corresponding to a label image onto disc204. Likewise, with respect to the OPU212, another laser driver236controls the firing and intensity of OPU laser beam246generated by OPU laser212to read data from and write data to the data side202of the optical disc204. Both the OPU212and OPH222can be implemented as photodetectors that provide laser focus feedback to their respective laser drivers236.

As noted above, disc drive system128additionally includes a mechanical coupling242that couples the OPU212on the data side202of optical disc204with the OPH222on the label side208of the disc. It is noted that the mechanical coupling242is not limited to a physical coupling between just the OPH222and OPU212. Rather, the mechanical coupling242may couple the OPH222to any component of the data-side laser assembly200or any component associated with the motion of OPU212(sled210) to achieve the same general purpose described herein of leveraging the OPU212positioning capability. The mechanical coupling242translates motion and positioning of the OPU212to motion and positioning of the OPH222. Thus, accurate positioning of the OPH222on the label side208of disc204depends upon the positioning capability of the OPU212. The OPU212has a precision radial positioning capability enabled by abundant positioning information inherent in the data tracks on the data side202of disc202. The mechanical coupling242leverages the positioning capability of the OPU212to enable accurate positioning of the OPH222and OPH laser224on the label side208of the disc202where there is typically no positioning information present.

FIG. 2provides a generic illustration of the mechanical coupling242. The generic mechanical coupling242shown inFIG. 2is intended to indicate a physical coupling between the data-side OPU212and label-side OPH222that provides a one-to-one correlation of motion and radial positioning of the OPU212to the OPH222. Thus, when the OPU laser beam246is positioned at the extreme inner-most radius of disc204, the OPH laser beam244is also positioned at the extreme inner-most radius of disc204. Likewise, when the OPU laser beam246is positioned at the extreme outer-most radius of disc204, the OPH laser beam244is also positioned at the extreme outer-most radius of disc204. However, as discussed in more detail below, a precise correlation of positioning between the OPU laser beam246and OPH laser beam244is also based on having zero average current offset applied to the fine actuator218of laser assembly200.

FIGS. 3 and 4illustrate one embodiment of a mechanical coupling242referred to herein as a rotary head-arm assembly300. Although the mechanical coupling242is discussed herein with primary reference to the rotary head-arm assembly300embodiment shown inFIGS. 3 and 4, this is not intended to be a limitation as to the type or manner of mechanical coupling242that may be appropriate for use in disc drive system128. To the contrary, various other types of mechanical couplings such as gear-train couplings, belt-drive couplings and other mechanical couplings between the OPU212and OPH222are also contemplated.

The rotary head-arm assembly300ofFIGS. 3 and 4includes a bottom-side or data-side arm302attached to the sled210through a first pivot joint304. As the sled210and OPU212move in a radial direction306along sled rails308and sled drive mechanism240, the motion of the sled210and OPU212is coupled through the data-side arm302and a second pivot joint310to a top-side or label-side arm312. As discussed in greater detail below, sled210is moved in the radial direction306by stepper motor228. The radial motion of the sled210and OPU212transfers through the label-side arm312to the OPH222attached to the label-side arm312toward the end that is opposite the second pivot joint310.

It is noted that, depending on the type of mechanical coupling242employed, there may be geometric and/or other anomalies present in the coupling that prevent a direct, one-to-one tracking of the motion and position of the OPH222with the motion and position of the OPU212. For example, in the rotary head-arm assembly300embodiment discussed above, it is apparent from the geometry of the head-arm assembly that a cosine error will be introduced in the positioning of the OPH222as it swings across the label side208of the disc204in the arc400(seeFIG. 4). Accordingly, there may be a radial positioning offset between the OPU212and OPH222introduced by a particular mechanical coupling implementation. However, mathematical algorithms executable as part of a print control application124, for example, can be introduced to eliminate such anomalies when positioning the OPH222for labeling a disc204. For example, a radial position offset between the OPU and OPH caused by a mechanical coupling between the OPU and OPH can be calculated and used to determine a target data track for the OPU that will match a desired starting radial position for the OPH to begin marking a label on the label side of the disc. One skilled in the art would readily recognize particular anomalies introduced by particular mechanical couplings, as well as appropriate algorithms to compensate for such anomalies.

Regardless of the type of mechanical coupling242used to couple the motion of the OPU212to the OPH222, accurate positioning of the OPH222on the label side208of disc204depends upon the positioning capability of the OPU212, as noted above. Positioning the OPU212on the data side202of disc204to a desired radial position (i.e., a target data track) is generally accomplished in two main steps. The first step in positioning the OPU212to a target data track involves a coarse positioning of the sled210(i.e., coarse actuator) using full-resolution steps from step motor228along sled rails308and sled drive mechanism240. Step motor controller248, stored in memory234and executable on processor232, first controls the step motor228to position the sled210(and OPU212, etc.) through full-resolution step sizes (e.g., 150 micron steps, approximately 125 data tracks per full step) at a radial position that is within approximately 125 data tracks (or less) of a target data track.

Once the step motor controller248has roughly positioned the sled210within the vicinity of the target data track (i.e., corresponding to the desired radial position for the OPH to begin labeling) through step motor228, the fine actuator controller250stored in memory234and executable on processor232performs a second positioning step to control the fine positioning of OPU laser beam246and to focus a laser spot directly onto the target data track. Fine actuator controller250controls the fine actuator218and, in turn, the OPU laser focusing lens216to provide fine positioning of OPU laser beam246in order to focus a laser spot onto the target data track.

Fine positioning is achieved by the fine actuator controller250serving power amplifier252up or down in the amount of output current being applied to fine actuator218. In general, fine actuator218functions to move focusing lens216in a radial direction242in small increments in between the larger movements from the sled210(i.e., coarse actuator). Fine actuator controller250servos the average current output of power amplifier252in a direction that positions OPU laser beam246directly at a target data track of disc204. Thus, after coarse positioning of sled210, the fine actuator controller250applies an average current offset to the fine actuator218through power amplifier252in order to precisely position the OPU laser beam246. Fine actuator218is typically capable of moving the laser spot of OPU laser beam246plus or minus approximately 200-300 tracks from its resting position, or zero-current position.

It should be apparent fromFIG. 2that only the first positioning step described above for positioning of the OPU212is applicable to positioning the OPH222on the label side208of disc204. That is, only the coarse positioning/motion of the sled210is coupled through mechanical coupling242up to the OPH222. The second, fine positioning step which moves the OPU laser246in small increments directly onto the target data track on the data side202of disc204provides no corresponding positioning or movement of the OPH222or OPH laser224on the label side of disc204. This is because the fine positioning provided by fine actuator218is not coupled through the mechanical coupling242to the OPH222, which is apparent from the illustration ofFIG. 2. The OPH222motion tracks only with the motion of the sled210, and not the motion of the OPU laser beam246being controlled by the fine actuator218on the sled210.

However, controlling fine positioning of the OPH222is achieved by microstepping the sled210with step motor228while monitoring (through a closed feedback loop) the sled position and the current offset being applied to the fine actuator218. Microstepping of step motors is well-known to those skilled in the art and will not be discussed in detail herein. In general, microstepping increases the position resolution of the sled210and is achieved through the step motor controller248electronically subdividing each full-resolution step of the step motor228into a larger number of smaller steps, or microsteps. Instead of applying a fixed positive or negative voltage to the stepper coils of step motor228, microstepping makes use of varying voltage levels to vary the step size.

As discussed above, during normal positioning of the OPU212and OPU laser214, feedback loop254provides a tracking error signal (e.g., positioning information of the sled210from the OPU212and current offset information from power amplifier252) used for fine positioning. Fine positioning of the OPU laser beam246is achieved first, by coarse positioning of the sled210as controlled by step motor controller248in order to get the sled210and OPU212to a data track that is near a target data track (i.e. using full-resolution steps). Second, the OPU focusing lens216and OPU laser beam246are fine positioned onto a target data track by the fine actuator controller250using the tracking error signal to servo the OPU laser beam246to a target position that is relative to the center of the target track (e.g., a target position that is at the center of the target track or near the center of the target track by some known offset amount) by applying current through the power amplifier in closed loop fashion. Accordingly, through the mechanical coupling242, the same tracking signal error and feedback loop254available for fine positioning the OPU laser beam246, is also useful in positioning the OPH laser224and OPH laser beam244on the label side208of the disc204. In general, the step motor controller248uses positioning information from the OPU212and fine actuator current information received through feedback loop254as the tracking error signal. Through feedback loop254, step motor controller248tries to drive the average fine actuator current to zero by issuing microstepping commands to the stepper motor228while maintaining the OPU laser beam246in a locked position on the target data track.

As an example, suppose a label to be placed on the label side208of disc204is to begin at a radial position determined from label image data that is generated by a label design application120and converted for rendering on concentric circular tracks by an image processing application122. A data track on the data side of disc204can then be determined (e.g., by print control application124) that is located at a radius that matches the desired radial position for beginning the label. Thus, the data track having a radius that matches the desired label radial position becomes the target data track that can be used to precisely position the OPH222and OPH laser224at the correct radial location to begin labeling the disc204.

In order to precisely position the OPH222and OPH laser224at the correct radial location, step motor controller248first controls step motor228to coarsely position sled210and OPU212within the vicinity of the target data track (i.e. using full-resolution steps to get within approximately 125 data tracks of the target track). The OPH222and OPH laser224move in correspondence with the sled210and OPU212through the mechanical coupling242as discussed above.

After this coarse positioning of sled210, the fine actuator controller250uses the tracking error signal generated by the normal data side servo optics and electronics to servo the OPU laser beam246to a target position relative to the center of the target track (e.g., a target position that is at the center of the target track or near the center of the target track by some known offset amount) by applying current through the power amplifier252in closed loop fashion. At this point it is noted that OPH222and OPH laser224are not positioned directly opposite of the target data track on the label side208of disc204, but are instead still positioned at a radial location corresponding to the coarse position of the sled210. In order to precisely position the OPH222and OPH laser224on the label side208of disc204and opposite of the target data track, the step motor controller248monitors the tracking error signal (i.e., the radial position of OPU laser beam246and the average current offset being applied to the fine actuator218) through feedback loop254. Step motor controller248then microsteps step motor228to move sled210in small increments toward the target data track. With each microstep, step motor controller248monitors the OPU laser beam246position through positioning information from the OPU212, and maintains a lock of OPU laser beam246on the target data track by instructing the fine actuator controller250to servo the OPU laser beam246to the center of the target track (i.e., a target position that is at the center of the target track or near the center of the target track by some known offset amount) by applying current through the power amplifier252to fine actuator218in closed loop fashion. Step motor controller248microsteps the sled210until the average current offset being applied to the fine actuator is zero, while the OPU laser beam246remains locked on the radial position of the target data track. At this point, it is apparent that the sled210, and the OPH222and OPH laser224(via the mechanical coupling242), will be positioned precisely at the target data track on the data side202, which is the desired radial position on the label side208.

Exemplary Methods

Example methods for positioning an optical print head (OPH)222at the non-data/label side of an optical disc will now be described with primary reference to the flow diagrams ofFIGS. 5 and 6. The methods apply generally to the exemplary embodiments discussed above with respect toFIGS. 1-4. While one or more methods are disclosed by means of flow diagrams and text associated with the blocks of the flow diagrams, it is to be understood that the elements of the described methods do not necessarily have to be performed in the order in which they are presented, and that alternative orders may result in similar advantages. Furthermore, the methods are not exclusive and can be performed alone or in combination with one another. The elements of the described methods may be performed by any appropriate means including, for example, by hardware logic blocks on an ASIC or by the execution of processor-readable instructions defined on a processor-readable medium.

A “processor-readable medium,” as used herein, can be any means that can contain, store, communicate, propagate, or transport instructions for use or execution by a processor. A processor-readable medium can be, without limitation, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples of a processor-readable medium include, among others, an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable-read-only memory (EPROM or Flash memory), an optical fiber (optical), a rewritable compact disc (CD-RW) (optical), and a portable compact disc read-only memory (CDROM) (optical).

Method500begins at block502, with generating a label image design to be rendered on a disc media such as an optical disc204. In an exemplary embodiment, a label design application120generates a label design user interface126for display on display device104. A user can then create a label image by specifying, or otherwise dragging-and-dropping text, a bitmap image, a digital photo, a graphic or symbol, and/or any combination thereof to create the label image on the user interface126.

At block504, the label image is converted into label image data that represents the label image. The label image data is then converted for rendering on concentric circular tracks of the optical disc. In an exemplary embodiment, an image processing application122processes the label image created with the label design user interface126to produce a data stream of label image data and laser control data to control rendering the image on concentric circular or spiral tracks of the optical disc204. The data stream is formatted as laser control data and is augmented with other control commands to control the disc media marking device102rendering a label on the optical disc204.

At block506, a radial position for beginning to write the label image is determined from the label image data. Subsequent track spacing from the radial position is also determined. In an exemplary embodiment, a print control application124determines the radius of the first label track and the subsequent label track spacing. After the radius of the first track and the track spacing are determined, the print control application124determines which label image data will correspond to each respective track and laser mark locations are specified in a coordinate system where concentric circular tracks are defined in coordinates of the radial distance and the distance along each respective track.

At block508, a target data track corresponding to the beginning radial position for the label is determined. Depending on the type of mechanical coupling242between the OPU and OPH, the radius of the target data track and the beginning radial position may correspond exactly, or they may correspond through a radial offset amount. This is because there may be geometric and/or other anomaly present in the mechanical coupling that prevents a direct, one-to-one tracking of the motion and position of the OPH222with the motion and position of the OPU212. The rotary head-arm assembly300embodiment is discussed herein above as an example of a mechanical coupling that introduces an error in the positioning of the OPH with respect to the positioning of the OPU. As noted above, mathematical algorithms executable as part of a print control application124, for example, can be introduced to eliminate such anomalies when positioning the OPH222for labeling a disc204. Thus, at block508, determining a target data track to correspond with the beginning radial position for labeling may involve determining a radial offset introduced by the mechanical coupling.

At block510of method500, after a target data track has been determined, a coarse positioner positions the sled/OPU to a data track that is near the target data track and within one or more full-resolution steps of the step motor228moving the sled210. Typically, this coarse positioning puts the sled/OPU to within approximately 125 data track or less of the target data track. The full-resolution steps of the step motor are controlled by a step motor controller248.

At block512, a fine positioner positions the OPU laser246directly on the target data track. Fine positioning of the OPU laser246is controlled by fine actuator controller250generating a feedback control signal output from power amplifier252which is applied to fine actuator218. Fine actuator218controls the motion of focusing lens216which is capable of moving the focus position of OPU laser beam246approximately plus or minus 200-300 tracks on the optical disc204from a zero offset current position.

Once the OPU laser246is locked onto the target data track, the step motor controller248again controls step motor228to microstep the sled/OPU to the target data track. Through feedback control loop254, step motor controller248monitors both the OPU laser246position (tracking signal error) to ensure it maintains a lock on the target data track, and the average offset current being applied to the fine actuator218, as indicated at block514.

Block516of method500continues atFIG. 6. At block516, the step motor controller248begins to incrementally microstep the sled/OPU in a direction toward the target track while monitoring (through feedback control loop254) the OPU laser246position and average offset current applied to the fine actuator218.

As indicated at block518, for each incremental microstep of the sled/OPU in a direction toward the target track (made by the step motor controller248controlling the step motor228), the fine actuator controller250, through feedback loop254, automatically adjusts the average current offset to the fine actuator218to maintain the OPU laser246in a locked position over the target track. It is apparent, that once the step motor228has been microstepped to where the average current offset is incremented to zero, the sled/OPU will be directly positioned at the target data track. In turn, through the mechanical coupling242between the OPU212and OPH222, the OPH222and OPH laser224will be precisely positioned at the beginning radial position for labeling the optical disc with the image label.

CONCLUSION