JP2007514267A - Improvement of optical density - Google Patents

Abstract

The optical density in the print medium (6) that becomes darker upon exposure to electromagnetic radiation, i.e. the area that appears to have maximum absorption for the user and appears black, is improved. The print medium (6) is divided (24) into at least one track (20). A defocused spot of electromagnetic radiation is formed in the track (20). The out-of-focus spot of electromagnetic radiation darkens the color of the print medium (6) in the track (20).

Description

RELATED APPLICATIONS This patent application is filed on September 12, 2003 and is incorporated by reference herein and is incorporated by reference. US Patent Application No. 10/660991, entitled “Optical Disc Drive Focusing Apparatus”, Attorney Docket No. This is a partial continuation application of No. 200311745. This application is also filed on Sep. 12, 2003, US patent application Ser. No. 10 / 661,394, assigned serial number “Optical disk Drive Focusing Apparatus” entitled “Optical disk Drive Focusing Apparatus”, which is incorporated herein by reference. Related to No. 200313592. This application is also filed on Sep. 12, 2003, US patent application Ser. No. 10 / 661,752, entitled “Optical disk Drive Focusing Apparatus,” filed on Sep. 12, 2003 and incorporated herein by reference. Related to No. 20031596.

FIELD OF THE INVENTION This invention relates generally to print media that become darker upon exposure to electromagnetic radiation, and more particularly to increasing the optical density of the print media.

BACKGROUND OF THE INVENTION Conventionally, optical discs are marked on the data side using a laser activated material to form dark spots that represent data. The dark spot is read by the optical disk drive. An optical disk drive emits light to the disk and reads data by detecting whether the light is reflected.

  In order to more fully utilize the available space on the optical disc, it is desirable to fit as much data as possible on the disc. In order to achieve this object, the spot size is reduced and the density of stored data is increased. The spot size is made as small as possible while maintaining the ability to read and write data accurately.

  In addition, an image may be labeled on the optical disc. Laser activated material is deposited on the label side of the disk. This laser activated material becomes dark, i.e., marked, when exposed to a laser in an optical disk drive.

  The length of time it takes to create or print a label on the laser activated material is a function of the rotational speed of the disk and the track width on the disk. The faster the rotation speed, the shorter the printing time, but there is an upper limit to the speed at which the label can be printed by rotating the disk.

  Conventionally, the printing time is shortened by increasing the width of the track, but there is an unmarked space between the tracks. In order to reduce the time required to create the label, this wide track is often spaced further than the width of the fully focused marking beam. Unmarked spaces are visually combined with marked spaces and appear as areas that are not fully marked. If the unmarked space is white or some other bright color and the marked space is black, the result obtained may not look completely black.

  A measure of the amount of light absorbed is optical density (OD). The region that appears to have the greatest absorption for the user is the region of OD1.2 that appears black. Higher OD values are possible, but for users, such values do not appear blacker. When a conventional wide track is used, the OD is often smaller than 1.2.

  Narrowing the track width increases the number of tracks per inch on the disk and reduces the unmarked space between the tracks, resulting in a darker image. However, narrowing the track width increases the surface area that the laser must cover, requiring a long print time. Thus, there is a trade-off between printing speed and OD. Labels printed using the prior art are made using a relatively narrow track and may have an OD of at least 1.2, but are made using a relatively wide track. It takes longer time to print than an OD label smaller than 1.2.

SUMMARY OF THE INVENTION In one embodiment, according to the principles of the present invention, the optical density of a print medium that becomes darker upon exposure to electromagnetic radiation can be improved. The print medium is divided into at least one track. A spot of electromagnetic radiation out of focus is formed in the track. Due to the out-of-focus spot of electromagnetic radiation, the color of the print medium in the track is darkened.

  This disclosure describes a method and apparatus for increasing the optical density of an optically labeled medium such as an optical disc. Experimental studies by the inventor have shown that optical labeling is achieved by defocusing the laser spot size, rather than using a focused laser spot, without reducing the linear velocity of the medium relative to the laser. It has been found that the size of the marking spot on the applied medium can be enlarged. According to these experimental results, it was found that the OD was improved by 30% at maximum when the track interval and the linear velocity were kept constant and the focus of the laser was shifted. This defocusing is done by generating an offset signal and adding it to the laser's focusing servo, which normally maintains a constant best focus as described in the relevant case. This focus offset method helps to recover large OD losses due to “dead space” created between “too far away” tracks. Further, according to the present invention, the OD can be improved without increasing the time required for labeling the medium.

  FIG. 1 shows an embodiment of a mass storage device 2 of the present invention. The mass storage device 2 is configured to be used with a mass storage medium 4 that is at least partially coated with a print medium 6.

  The mass storage medium 4 is an arbitrary medium capable of storing information. In one embodiment, the mass storage medium 4 is an optical disk.

  The print medium 6 is any medium on which an image can be printed by exposure to electromagnetic radiation. The print medium 6 becomes darker or brighter when exposed to electromagnetic radiation, changes its reflectivity, or changes its optical properties. In one embodiment, the print medium 6 covers at least a portion of the mass storage medium 4. The print medium 6 is divided into at least one track 20. In one embodiment, the track 20 is a spiral track on the mass storage medium 4. In an alternative embodiment, the track 20 is a concentric ring on the mass storage medium 4.

  In one embodiment, the mass storage device 2 includes an electromagnetic radiation source 8, a focus detector 10, an offset controller 12, and a radial positioning device 14, optionally including a computer 16 and a program storage system 18. In addition.

  The electromagnetic radiation source 8 is any device that is configured to generate electromagnetic radiation that is emitted toward the track 20 of the print medium 6. In one embodiment, the electromagnetic radiation source 8 is a laser radiation source that emits a coherent beam of electromagnetic radiation having a wavelength of 780 nanometers.

  The focus detector 10 is any combination of hardware and executable code configured to find the focal length between the electromagnetic radiation source 8 and the print medium 6. In one embodiment, this focal length is the distance from the print medium 6 when the electromagnetic radiation source 8 forms a focused spot of electromagnetic radiation on the print medium 6.

  The offset controller 12 is any combination of hardware and executable code configured to determine the focus offset of the electromagnetic radiation source 8 and communicate the focus offset to the radial positioning device 14.

  The radial positioning device 14 positions the electromagnetic radiation source 8 at a focal length position shifted from the print medium 6 by a focal offset, and is configured to form a defocused electromagnetic radiation spot in the track 20. Hardware and executable code. Due to the defocused spot, the color of the print medium 6 in the track 20 becomes darker. The spot size of the defocused spot is larger than the conventional focused spot size.

  Computer 16 is any combination of hardware and executable code configured to execute executable code stored in program storage system 18. Although the focus detector 10 and the offset controller 12 are illustrated and described as separate from the computer 16, in alternative embodiments, they may be integrated with the computer 16, or some of them.

  Program storage system 18 is any device or system configured to store data or executable code. The program storage system 18 is also a program storage system that specifically implements a program, applet or instruction executable by the computer 16 for performing various steps of the method of the present invention executable by the computer 16. Also good. Program storage system 18 may be any type of storage medium, such as a magnetic storage medium, an optical storage medium, or an electronic storage medium.

  In FIG. 1, the program storage system 18 is depicted as a single device. Alternatively, program storage system 18 may include multiple devices. Also, each device of program storage system 18 may be implemented with different media types. For example, one device of program storage system 18 may be a magnetic storage medium and another device of program storage system 18 may be an electronic storage medium.

  FIG. 2 is a flow diagram illustrating the steps of one embodiment of the present invention. Although the steps shown in FIG. 2 are described in a specific order, the present invention also includes variations of the order of steps. Further, another step may be further implemented between the steps shown in FIG. 2 without departing from the scope of the present invention.

  The print medium 6 is divided (24) into at least one track 20. In one embodiment, the print medium 6 is divided (24) into a plurality of concentric tracks 20. In an alternative embodiment, the print medium 6 is divided into spiral tracks 20.

  A defocused spot of electromagnetic radiation is formed 26 in the track 20. The defocused spot darkens the color of the print medium 6 in the track 20 (28) or changes its optical properties. In one embodiment, this defocused spot of electromagnetic radiation is formed (30) by determining the focal length between the electromagnetic radiation source 8 and the print medium 6, as shown in FIG. A focus offset is applied (32) to the focal length. The focus offset may be any distance that achieves the desired effect (see FIGS. 4-6 for examples). In one embodiment, the focus offset is any distance of at least 20 microns. In other embodiments, the focus offset is any distance less than 80 microns.

  The electromagnetic radiation source 8 is positioned (34) at a focal length position shifted from the print medium 6 by a focal offset. The electromagnetic radiation source 8 generates (36) electromagnetic radiation towards the print medium 6. The focus offset is a positive or negative magnitude distance (see FIG. 4).

  In one embodiment, the step of determining (30) the focal length between the electromagnetic radiation source 8 and the print medium 6 comprises printing when the electromagnetic radiation source 8 forms a focused spot of electromagnetic radiation on the print medium 6. Determining (30) the distance from the medium 6; Several different focusing algorithms may be used. The focal distance to the print medium 6 may be obtained using a feedforward algorithm or an adaptive servo algorithm using a table described in the related application.

  FIG. 3 is a flow diagram illustrating the steps of another embodiment of the present invention. Although the steps shown in FIG. 3 are described in a specific order, the present invention includes those in which the order of the steps is changed. Further, further steps may be performed between the steps shown in FIG. 3 without departing from the scope of the present invention.

  The focal length between the electromagnetic radiation source 8 and the print medium 6 is determined (30). The electromagnetic radiation source 8 is positioned (34) at a focal length shifted from the print medium 6 by a focal offset. A focus offset is a positive or negative magnitude distance.

  In one embodiment, the focal distance between the electromagnetic radiation source 8 and the print medium 6 is the distance from the print medium 6 when the electromagnetic radiation source 8 forms a focused spot of electromagnetic radiation on the print medium 6. It can obtain | require (30) by calculating | requiring (30). As mentioned above, some of a number of alternative methods for determining the distance from the print medium 6 to the radiation source 8 are disclosed in the related application.

  The electromagnetic radiation source 8 generates (36) electromagnetic radiation toward the print medium 6 to form a defocused spot of electromagnetic radiation in the track 20. The spot shifted in focus darkens the color of the print medium 6 in the track 20 (28).

  One advantage of the system and method of the present invention is that the optical density of the print media can be improved without sacrificing speed. When marked using a defocused spot, the track is marked at the same speed as using a focused spot of electromagnetic radiation, but with a higher optical density.

  For example, in order for the print medium 6 that is activated, i.e. written, by light or other electromagnetic energy to obtain a maximum optical density (OD), an optimum radiation intensity over a certain period of time is required. In the case of a focusing system, especially in the case of a system with a large numerical aperture (such as a compact disc system or a DVD system), the spot size on the print medium 6 is reduced by a slight deviation in the focal length of the objective lens (by the radial positioning device 14). It changes a lot. By shifting the focal point (Z-axis direction) distance of the objective lens from the minimum spot size focal length by a specified amount, the optical density can be greatly improved. Experimental tests have shown that the optical density increases by 30% to 100%.

  As an example of data, FIGS. 4 and 5 show the focus offset in the Z-axis (focal length) direction of the radial positioning device 14 when the track density is 1040 tracks / inch and the linear velocity of the laser is 0.5 m / second. The relationship with the change of OD is shown. FIG. 4 shows the relationship between offset and OD change when the laser output is 45 milliwatts, and FIG. 5 shows the relationship between offset and OD change when the laser output is 70 milliwatts. The delta OD is a difference between the OD of the non-mark area and the OD of the mark area. The average OD is the overall OD from the mark surface. As the track width is increased to include the area between the tracks (see FIG. 6), the non-mark area decreases, and the average OD increases to the vicinity of the OD of the mark area itself. As you can see, Delta OD and Average OD have very similar trajectories.

  FIG. 6 is a collection of experimental images of test print media 6 using a 70 milliwatt laser (radiation source 8) on which tracks 20 with a track spacing of 1040 tracks / inch were written at a track speed of 0.5 m / sec. is there. Further, a spot size 40 indicating a single pixel is also drawn next to the track 20. As can be seen from the example without offset, the tracks are separated by a large distance. However, when shifting the focus, as the offset distance increases in the negative direction, the OD increases up to about −50 μm, at which point the output / area magnitude at the defocus is It will not be able to mark properly. As shown in FIG. 5, the OD significantly decreases up to −60 μm. The figure also shows the effect when the focus is offset in the positive direction. When the laser output is set to 70 milliwatts, the OD actually decreases as the positive offset increases, as shown in FIGS. However, the OD actually increases when the laser power is as low as 45 milliwatts, as in FIG. However, the OD decreases as the offset further increases. As will be appreciated by those skilled in the art, the actual offset distance at which the OD is maximized depends on the print medium 6, the electromagnetic radiation source 8, the corresponding power level, and the speed of the print medium 6 relative to the electromagnetic radiation source 8. 4-6 are only used to illustrate one particular embodiment as an example.

  The above descriptions are merely examples of some embodiments of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the scope of the invention. For example, the print medium may be rotated by a motor with respect to the radiation sources 8 arranged radially. Alternatively, the radiation source 8 may be moved relative to the print medium 6 while the print medium 6 is stationary. The print medium 6 may be a material other than the optical disk. Accordingly, the present invention includes all such alternatives, modifications and variations that fall within the scope of the appended claims.

FIG. 4 is a diagram of a mass storage device with a radial positioning device configured to defocus an electromagnetic radiation source in accordance with the present invention. FIG. 3 is a flow diagram illustrating one embodiment of a method of the present invention that improves the optical density of a print medium that becomes darker upon exposure to electromagnetic radiation. FIG. 6 is a flow diagram illustrating another embodiment of the method of the present invention using an electromagnetic radiation source to improve the optical density of a print medium that becomes darker when exposed to electromagnetic radiation. It is a graph which shows the relationship between an optical density in case a laser output is 45 milliwatts, and a focus offset. It is a graph which shows the relationship between an optical density in case a laser output is 70 milliwatts, and a focus offset. FIG. 2 is a group of images of print media showing multiple tracks and spot sizes at various focus offsets when using 70 milliwatt laser power.

Claims (10)

A method of improving the optical density of a print medium (6) that becomes darker when exposed to electromagnetic radiation,
Dividing the print medium (6) into at least one track (20);
Forming a defocused spot of electromagnetic radiation in the at least one track (20);
A method wherein the defocused spot of electromagnetic radiation darkens the color of the at least one track (20).   The step (24) of dividing the print medium (6) into at least one track (20) comprises dividing the print medium (6) into a plurality of concentric tracks (20). Method.   The method of claim 1, wherein dividing (24) the print medium (6) into at least one track (20) comprises dividing the print medium (6) into spiral tracks (20). . Forming the defocused spot of electromagnetic radiation (26),
Determining a focal length between the electromagnetic radiation source (8) and the print medium (6) (30);
Positioning the electromagnetic radiation source (8) at a position of the focal length shifted from the print medium (6) by a focal offset;
Generating electromagnetic radiation from the electromagnetic radiation source (8) towards the print medium (6). A mass storage device (2) used together with a mass storage medium (4) comprising a print medium (6) covering at least a part of the mass storage medium (4), the print medium (6) Is darkened by exposure to electromagnetic radiation and is divided into at least one track (20), said mass storage device (2) being
An electromagnetic radiation source (8) configured to generate electromagnetic radiation toward at least one track (20) of the print medium (6);
A focus detector (10) configured to determine a focal length between the electromagnetic radiation source (8) and the print medium (6);
The electromagnetic radiation source (8) is positioned at the focal length position shifted from the print medium (6) by a focal offset to form a defocused electromagnetic radiation spot in the at least one track (20). A radial positioning device (14) configured in such a manner that the defocused electromagnetic radiation is configured to darken the color of the print medium (6) in the at least one track. Capacity storage device (2).   The mass storage device (2) of claim 5, further comprising an offset controller (12) configured to determine the focus offset and communicate the focus offset to the radial positioning device (14). .   The mass storage device (2) according to claim 5, wherein the electromagnetic radiation source (8) comprises a laser light source.   The focus detector (10) determines a distance from the print medium (6) when the electromagnetic radiation source (8) forms a focused spot of electromagnetic radiation on the print medium (6). The mass storage device (2) according to claim 5, further comprising: A method of using an electromagnetic radiation source to improve the optical density of a print medium (6) that has been blackened by exposure to electromagnetic radiation and divided (24) into at least one track (20), comprising:
Determining a focal length between the electromagnetic radiation source (8) and the print medium (6) (30);
Positioning the electromagnetic radiation source (8) at a position of the focal length shifted from the print medium (6) by a focal offset;
Generating electromagnetic radiation from the electromagnetic radiation source (8) toward the print medium (6) to form a defocused spot of electromagnetic radiation in the at least one track (20);
The defocused spot darkens the color of the print medium (6) in the at least one track (20). The step (30) of determining a focal distance between the electromagnetic radiation source (8) and the print medium (6) comprises the step of determining the electromagnetic radiation in which the electromagnetic radiation source (8) is focused on the print medium (6). 10. A method according to claim 9, comprising determining a distance from the print medium (6) when forming a spot.

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