WO2002084660A1

WO2002084660A1 - Sensing disk centering

Info

Publication number: WO2002084660A1
Application number: PCT/US2002/010695
Authority: WO
Inventors: Ronald David Andrewlevick; Laurence Frederick Platt
Original assignee: Thomson Licensing S.A.
Priority date: 2001-04-17
Filing date: 2002-04-04
Publication date: 2002-10-24

Abstract

A method for determining concentric placement of an optical disk about an axis prior to processing, comprising the steps of; sensing the disk location with a plurality of non-contact sensors positioned radially about the axis; initiating the processing in accordance with the plurality of non-contact sensors indicating the concentric placement of the disk about the axis; and, inhibiting the processing in accordance with any one of the plurality of non-contact sensors indicating an absence of the disk.

Description

SENSING DISK CENTERING

This invention relates to the field of non-contact sensing and in particular to the determination of concentric positioning of optical disks. BACKGROUND OF THE INVENTION

At various stages in the manufacture of optical disk media it is necessary to determine the concentric or coaxial placement of the disk medium prior to initiating a manufacturing step. The result of such concentricity determination can be employed to initiate the process, if within acceptable limits, or to correct misplacement or halt the process for manual intervention. In a particular optical disk manufacturing process a pattern is embossed in a lacquered disk surface. An example of such pattern embossing is shown in United States Patent 5,533,002. A problem can occur when a disk to be embossed is transferred from a disk storage spindle to an embossing carousel and mis-positioned on the disk carrier or station. Such non-coaxial disk positioning not only renders the disk un-saleable but also results in costly damage to the disk carrier and associated mechanisms.

In an exemplary embossing apparatus, having for example multiple disk carriers, sensing is provided at various stages of the embossing process. An initial test is performed when a vacuum picker retrieves a disk from a supply spindle and places the disk on a carrier for subsequent embossing. A failure to establish a vacuum is signaled to the embossing control system as a disk absence. Having established that the disk is present the disk carrier and disk move to locate the disk at a pre-embossing position where disk further sensing is performed to determine disk presence or absence. A sensed disk absence, signals the associated embossing control logic which halts the embossing process and alerts an operator. However, this sensor detects only disk presence or absence and thus will signal a non-concentrically located disk as a disk presence and allow potentially destructive consequences to ensue.

A first attempt to remedy disk to carrier misalignment uses a tapered tip mandrill which is inserted through a central hole in the disk carrier and into the hub or center of the disk. The tapered mandrill tip causes each disk to be centered or rendered coaxial with the carrier at the pre-embossing process position. This centering method requires modification to the disk carrier and provision of control and actuating mechanism for mandrill insertion and retraction. The mechanical modifications required to facilitate mounting of the mandrill and actuator render the carrier non-standard and thus non-interchangeable within a range of similar disk processing equipment. Furthermore, because this centering method is applied to every disk, processing cycle time is increased at this manufacturing step. At various stages in the manufacture of optical disk media non-concentric disk placement must be identified and remedied. Thus a system is required to evaluate and determine concentric or coaxial disk placement prior to initiating a manufacturing step. Such a measurement system is required to determine positioning to a predetermined degree of accuracy, to enable concentricity determination to be performed without disk contact and without significant process constraint.

SUMMARY OF THE INVENTION A disk placement evaluation system employs an advantageous method for determining concentric placement of an optical disk about an axis prior to processing. The method comprises the steps of, sensing the disk location with a plurality of non- contact sensors positioned radially about the axis, initiating the processing in accordance with the plurality of non-contact sensors indicating the concentric placement of the disk about the axis; and, inhibiting the processing in accordance with any one of the plurality of non-contact sensors indicating an absence of the disk.

A further evaluation system employs a method for determining placement of an optical disk about an axis prior to processing. The method comprises the steps of, illuminating a disk location with multiple focused light beams positioned radially about the axis; and generating logic signals responsive to each of the multiple light beams reflected from a disk positioned at the disk location; and determining disk alignment relative to the axis by analyzing the logic signals to enable processing when aligned and inhibiting processing when mis-aligned.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an inventive arrangement for non-contact sensing of an optical disk.

Figure 2A shows a further view of the inventive arrangement shown in Figure 1.

Figures 2B and 2C show various optical disk placements relative to the inventive sensing arrangement of Figure 1. Figures 3A and 3B show a logic arrangement for processing sensor signal to determine concentric disk placement.

Figure 4 illustrates a further inventive arrangement for correcting disk placement. Figure 5 is sequence for evaluating sensor signals to determine process control based on disk concentricity.

DETAILED DESCRIPTION In an inventive arrangement disk to carrier alignment can be determined by non-contact sensing employing for example, interrupted or reflected light sensing, alignment pattern detection, etc. In FIGURE 1 three non-contact sensors, 100, 120, 140 are radially located about an axis Ax of a carrier 50 and spaced from each other by 120 degrees, as depicted in FIGURE 2. The radial distance of each sensor is chosen to locate, detect or observe an edge of a disk when position coaxially or concentrically with axis Ax of disk carrier 50. Three non-contact optical sensors, shown FIGURE 1 , comprise fiber optic amplifiers, 110, 130 and 150 respectively which are coupled via an optical fiber to the fiber optic emitter receiver sensors 100, 120, 140 located on a mounting plate or radial arms 80. The optic amplifiers supply power to the optical emitter and process the optical receiver output signal to form logical output signals at the amplifier output. Sensors 100, 120, 140 are positioned to emit a beams of light which form focused spots that illuminate specific locations on a concentrically positioned disk. For example, in FIGURE 2A the individual beams of light are arranged to illuminate a specific area of a 120 millimeter disk approximately 1 millimeter from the disk edge, a location termed diameter 119. If a disk is present the illuminating spot is reflected from the disk surface and received by the receiver sensor which generates an electrical signal in proportion to the intensity of the reflected illumination.

If the disk is absent or mis-aligned relative to sensor heads 100, 120, 140, significantly less illuminating beam is reflected from the carrier and received by the receiver sensor as reduced amplitude signal. The sensor output signals are processed by amplifiers, 110, 130 and 150 to form logical signal levels at the outputs of amplifiers, 110, 130 and 150, based on the reflected light intensity. For example, a detected disk condition can be represented by a high level signal or logical 1 state, with an undetected condition being represented by low level signal or logical 0 state. These logical signals can be coupled to a logic arrangement for example, the AND function depicted in FIGURE 3 or a microcontroller (not shown). The microcontroller can determine from the logical states of the three sensor signals a disk presence, disk absence, or non concentric disk positioning. In response to sensor signal analysis the microcontroller can initiate various control sequences. For example, if the disk is present and concentrically positioned an exemplary embossing process step can be performed. If a disk is missing the controller can halt further processing and generate an alarm. In addition sensed non-concentric disk placement can be processed to determine the direction required to restore concentric placement.

The radial location of illuminating beams from sensor heads 100, 120, 140 is depicted in FIGURE 2A for a disk concentrically located about axis Ax. FIGURE 2B shows a disk non-concentrically placed such that two of the three spot beams are reflected, and FIGURE 2C shows additional non-concentricity such that only of the three spot beams is reflected back to the receiver sensor.

The logical output signals from amplifiers, 110, 130 and 150 can be coupled for analysis by the logic arrangement shown in FIGURE 3A which can differentiate between concentric and non-concentricity disk placement. In the truth table, shown in FIGURE 3B associated with the AND function of FIGURE 3A, a logical 1 results when all the sensors indicate a disk presence which as a consequence of the illuminating spot size and location within 1 millimeter of the disk edge signifies that the disk is concentrically placed. Thus a logical 1 enables the initiation of a processing step, for example embossing a pattern into the disk surface. If one sensor fails to indicate a disk presence the output from the AND gate is a logical 0 or low and the exemplary process step is halted, for example, pending manual intervention.

Clearly a combination of logic gates, or a microcomputer can be employed to analyze the sensor output signals and determine for example a) all outputs = 0, disk absent, b) all outputs = 1 , disk present and substantially aligned, as shown in FIGURE 2A, c) 2 outputs = 1 , one output = 0, disk positioned before sensor generating the logical 0 output signal, as shown in FIGURE 2B, d) one output = 1 , 2 outputs = 0, disk positioned under and or beyond the sensor generating the logical 1 output, shown in FIGURE 2C. It can be seen that with logical analysis of the three sensor signals it is possible to determine significantly more than disk presence or absence. For example, when all outputs =1 , the disk is not only present but it is substantially aligned. Furthermore, not only can non-coaxial positioning be determined, directional misalignment can be inferred and appropriate corrective disk manipulation applied either manually or automatically to achieve a substantially aligned condition. For example, the analyzed sensor signals can be employed to illuminate indicators In, depicted in FIGURE 2A which can show the direction of mis- alignment. Furthermore such sensor analysis can provide a real time indication of successful corrective alignment by means of a suitable indication either visually by flashing the mis-alignment indicators or by suitable acoustic cue, for example, a tone blip. In addition, because the disk position is sensed, corrective manipulation need only be applied when required thereby avoiding loss of cycle time by unnecessary disk realignment.

Directional misalignment can be inferred from sensor analysis thereby allowing appropriate corrective disk manipulation to be applied, for example, by multiple by recursive adjustments. However, such recursive alignment methods are potentially wasteful of process time. In a further inventive arrangement the sensor signals are analyzed, for example as depicted in the flow chart shown in figure 5, to determine that at least one sensor is "ON", indicating that a disk is present but not coaxially positioned on the carrier. This non-directional determination of misalignment can be employed to activate a centering arrangement which, in addition is logically controlled to permit corrective centering only when the disk carrier is stationary. The centering device can be positioned at the center of the three sensor arrangement directly above the disk hub or center hole. When activated, i.e. carrier stopped and disk misaligned, the centering arrangement is moved downward into the hub and expanded, spreading at least three limbs in radial directions away from the carrier axis. The radial displacement of the limbs is limited to the nominal radius of the disk hub, in this way the disk is repositioned to be coaxially located about the carrier axis. Immediately following limb spreading the limbs are retracted and the mechanism is elevated from the disk hub. The mechanism can be considered a modified form of multi section tong which provides both length extension and end or limb closure or expansion. Figure 4 depicts, in simplified form, a pair of centering limbs, however a third limb or a second pair of limbs are employed to provide corrective centering motion. In FIGURE 4, lever ends A and B are drawn towards each other causing a similar closing motion at hinges a and b, accompanied by a lengthening downward motion depicted by arrows aa and bb. Movement at hinges a and b cause limbs A and B to pivot at hinge C causing limbs A and B to separate or spread. Thus the mis-centered inner hub surface closest to the carrier axis is contacted first by the spreading limb and propelled away from the center of the carrier until the maximum spread or limb separation is reached and the disk is centered. Maximum limb spread is made equal to the diameter of the hub and can be determined, for example, by the deflection of terminal ends A and B. For example each end can be driven by crank pins mounted on a drive wheel of a specific diameter. Terminal ends A and B can be moved by a double action cylinder or magnetic solenoids. Maximum limb spread can also be determined by limiting deflection or range of motion of hinges a and b. In the inventive arrangement non-contact sensing is provided by three fiber optic emitter receiver amplifiers that form logical output signals. A logic device analyzes the output signals to determine disk alignment relative to the axis and control disk processing such that processing is enabled when the disk is aligned and inhibited when the disk mis-aligned.

Claims

1 1. A method for determining concentric placement of an optical disk about an

2 axis prior to processing, comprising the steps of:

3 sensing said disk location with a plurality of non-contact sensors positioned radially about said axis;

5 initiating said processing in accordance with said plurality of non-

6 contact sensors indicating said concentric placement of said disk about said axis;

7 and, β inhibiting said processing in accordance with any one of said plurality

9 of non-contact sensors indicating an absence of said disk.

1 2. The method of claim 1 , wherein sensing step comprises spacing said coaxially

2 positioned plurality of non-contact sensors at a common radial distance from said

3 axis.

i 3. The method of claim 1 , wherein sensing step comprises spacing said coaxially

2 positioned plurality of non-contact sensors by a common angle there between.

1 4. The method of claim 2, wherein spacing step comprises locating said

2 coaxially positioned plurality of non-contact sensors symmetrically adjacent a

3 circumference of said disk.

i 5. The method of claim 2, wherein spacing step comprises locating said

2 coaxially positioned plurality of non-contact sensors with a radial distance for

3 sensing adjacent to a perimeter of said disk.

1 6. The method of claim 1 , wherein inhibiting step comprises signaling a disk absence if all of said plurality of non-contact sensors indicate a disk absence.

7. The method of claim 1 , wherein inhibiting step comprises signaling a non- coaxial disk placement about said axis when any one of said plurality of non- contact sensors indicates a disk absence.

8. The method of claim 7, wherein signaling step comprises determining a direction of said non coaxial disk placement about said axis by analyzing said any one of said plurality of non-contact sensors indicating a disk absence.

9. The method of claim 8, wherein determining step comprises manipulating said disk in accordance with said determined direction to eliminate said non coaxial disk placement about said axis.

10. The method of claim 1 , wherein initiating step comprises applying a vacuum to secure said disk in said sensed coaxial location.

11. A method for determining placement of an optical disk about an axis prior to processing, comprising the steps of: illuminating a disk location with multiple light beams positioned radially about the axis; generating logic signals responsive to each of the multiple light beams reflected from a disk positioned at the disk location; determining disk alignment relative to the axis by analyzing the logic signals to enable processing when aligned and to inhibit processing when mis- aligned.

12. The method of claim 11 , wherein said analyzing step includes indicating a mis-alignment direction.

13. The method of claim 11 , wherein said analyzing step includes signaling correction of a disk mis-alignment.

14. The method of claim 11 , wherein said illuminating step includes lighting the disk location at a predetermined distance from the axis.

15. The method of claim 11 , wherein said illuminating step includes lighting the disk location with at least three light beams.

16. The method of claim 11 , wherein said illuminating step includes lighting an area adjacent to an edge of a disk positioned at the disk location.

17. An apparatus for determining placement of an optical disk about an axis prior to processing, comprising: a plurality of optical emitters positioned radially about the axis, each illuminating a disk location with a beam of light; a plurality of optical receivers each generating a logic signal responsive to the light beam reflected from a disk surface positioned at the disk location; and, a logic arrangement receiving and analyzing each logic signal and determining disk alignment relative to the axis, the logic arrangement enabling processing when the disk is aligned and inhibiting processing when the disk mis- aligned.